can normal force do non zero work?and can kinetic energy of a sysytem be increased without applying any external force?

Normal force can do no-zero work, for ex if the object is in equilbrium. It would be wrong if i say KE cannot be increased without applying any external force. this is possible in cases such as that of gravitational force. In some cases, it isn’t just about acceleration  if you see notice things. Because as we know KE is never constant, so they could be increased or decreased usually by applying a force.